Gas oil cuts, whether straight run from a crude petroleum or from a catalytic cracking process, currently still contain non negligible quantities of aromatic compounds, nitrogen-containing compounds and sulphur-containing compounds. The current legislation of the majority of industrialised countries dictates that engine fuel must contain less than 500 parts per million (ppm) of sulphur. Some countries have no current regulations which impose a maximum aromatics and nitrogen content. However, several countries or states, like Sweden and California, are known to be planning to limit the aromatics content to less than 20% by volume, or even to less than 10% by volume, and some experts believe that this limit could be 5% by volume. In Sweden in particular, certain classes of diesel fuel must already satisfy very severe specifications. Thus in that country, class II diesel fuel cannot contain more than 50 ppm of sulphur and more than 10% by volume of aromatic compounds, and that of class I cannot contain more than 10 ppm of sulphur and 5% by volume of aromatic compounds. Class III fuel in Sweden must currently contain less than 500 ppm of sulphur and less than 25% by volume of aromatic compounds. Similar limits also apply for the sale of that type of fuel in California.
During this time, motorists in several countries have pressed for legislation which will oblige gasoline producers to produce and sell a fuel with a minimum cetane number. Current French legislation requires a minimum cetane number of 49, but in the near future this minimum number could be at least 50 (as is already the case for class I fuel in Sweden), and probably at least 55; most probably it will be between 55 and 70.
A number of specialists are of the serious view that in the future the nitrogen content will be regulated, to less than 200 ppm, for example, or even less than 100 ppm. A low nitrogen content would improve the stability of the products, which would be welcomed by both the product vendor and the producer.
A reliable and efficient process thus needs to be developed, which process can produce a product with improved characteristics regarding the cetane number and the aromatics, sulphur and nitrogen content, from conventional straight run gas oil cuts or those from catalytic cracking (LCO cut) or from a different conversion process (coking, visbreaking, hydroconversion of residues, etc.). It is particularly important, and this is one of the advantages of the process of the present invention, to produce a minimum of gaseous hydrocarbon compounds and to be able to produce an effluent which is directly and integrally saleable as a very high quality fuel cut. Further, the process of the present invention can be conducted over a long period of time without the need for regeneration of the catalysts used, which have the advantage of being very stable over time.